1. Field of the Invention
The present invention relates to a bicycle hub drive system with a clutch that allows a bicycle rider to easily engage and disengage the hub drive system of the bicycle.
2. Description of the Prior Art
In a conventional bicycle drive system a rider powers the bicycle by applying force through the rider's feet to the bicycle pedals which are mounted on a crank arm to a large sprocket which drives a chain loop in rotation in a forward direction. The chain is engaged with a smaller sprocket that is coupled to the hub of the rear bicycle wheel.
There is a recognized desire among many riders of trick bicycles to have a rear wheel which is capable of being entirely disengaged from the drive train. With a conventional free wheel ratchet mechanism the rider is forced to backpedal constantly to allow the rear bicycle wheel to rotate in reverse. Since the rider's weight is predominantly carried by the pedals, this constant backpedaling can upset the rider's balance. It also makes some tricks much harder to perform than would otherwise be the case.
There are conventional systems that allow a rider to disengage the drive sprocket from the hub. Such systems operate by means of a clutch hub which only engages the drive when the rider pedals in a forward direction. The hub begins disengagement from the drive sprocket when the forward force applied to the bicycle pedals ceases. Deliberate backpedaling by the rider at this point will cause the clutch to become fully disengaged. Once fully disengaged the hub is free to rotate in either direction without any effect on the positions of the bicycle pedals.
Existing bicycle clutch designs of this type typically employ a jamming cone which is moved axially to jam in a conical seat. However, the axial movement required is typically created using a drive thread. Drive threads are difficult to manufacture and are also expensive. Furthermore, the axial movement of the clutch parts creates large axial loads which are undesirable. Furthermore, the action is also generally poor.
Another problem with conventional clutches of this type is that the hub runs on a bearing fitted to the outside of the driver. Such a construction results in large bearing sizes and an undesirable “nested” bearing arrangement. Other types of bearing arrangements are impractical due to the large amount of space required by the mechanism.
While some bicycle clutches have been devised that utilize a radial movement of rollers, the intricacies of the design and the restricted space have resulted in very high contact stresses. These excessive stresses lead to premature failure and poor reliability and function. Furthermore, clutches of this type are quite expensive to produce.